You can discard most of the output. For you, only this part is interesting:

keycode 116 (keysym 0x0, NoSymbol)

This tells you all you need to know: the keycode, the keysym and if and how that key is mapped.
Now that you know the key you want to map, you can create your .xmodmaprc file.
Copy the following line into the .xmodmaprc file:

xmodmap -e keycode 116=Multi_key

Change the keycode to the one that was outputted when you ran xev.

If you want this change to be permanent, add the following line into your shell startup script. For our example, we'll use .bashrc: